Position measurement of high-energy e-beams for pattern placement improvement

We have developed a technique based on use of a novel e-beam detector to enhance pattern placement accuracy of high-performance e-beam tools in the patterning of membrane masks. The detector consists of a reverse biased Schottky diode whose area coincides with that of the membrane, and which is placed immediately behind the membrane/-absorber/resist multilayer. An accurately patterned absorber overlayer covers the detector surface. The overlayer absorbs a fraction of the incident electrons, modulating the detector signal as the beam passes over the membrane. We have studied and modeled the performance of prototype detectors covered with 16 micrometers period gratings over an incident energy range of 5-50 keV. The combination of Schottky diode and patterned overlayer has been used to improve electron scattering models. We have observed excellent SNR with a 40 nC/cm2 dose at 50 kV, and spatial resolution better than 0.1 micrometers of a beam transmitted through a membrane. More accurate position information can be obtained by taking a Fourier transform of the diode current waveform created as the incident beam traverses several grating periods. In a poor operating environment, we have observed phase accuracy in 100 micrometers fields of +/- 4 degrees. We have developed an algorithm capable of processing pattern-based data sets at high speeds and low information storage requirements. This technique can be easily implemented with little overhead and little modification of existing systems.